Ternary representation of contextual information along the CA1 transverse axis

Episodic memory refers to the recollection of personally experienced events anchored in spatial contexts. Salient objects within a navigation environment serve as both landmarks and event cues; however, the nuanced integration of these elements during episodic memory formation is not well understood. The mnemonic functions of the hippocampal CA1 region are partially organized along its transverse axis, with proximal and distal subregions preferentially processing spatial and non-spatial information, respectively. Based on comprehensive analysis of neuronal responses along the CA1 proximodistal axis to manipulations of environmental cues and object features, we identified an event-like population coding within CA1 following object displacement. In addition, the neuronal responses at both initial and relocated object locations were shaped by distinct convergent inputs. These findings highlight the specific roles that objects may play in spatial navigation and memory encoding, providing novel insights into the selective processing of object-related information within the entorhinal-hippocampal network. Significance StatementSalient objects within a navigation environment serve as both landmarks and event cues critical for episodic memory. However, the enigmatic contribution of objects to the "where" and "what" components of episodic memory remains poorly understood. Here we comprehensively analyzed the neuronal responses in the hippocampal CA1 region along its transverse axis, to manipulations of environmental cues and object features. Our results revealed an event-like population coding within CA1 following object displacement, suggesting a minimal landmark role these objects play during memory formation. This study provides novel insights into the selective and flexible processing of object-related information within the entorhinal-hippocampal network.